User's Manual

In the above example, if a hearing aid meets the M2 level rating and the wireless
phone meets the M3 level rating, the sum of the two values equal M5. This
should provide the hearing aid user with “normal usage” while using their
hearing aid with the particular wireless phone. “Normal usage” in this context is
defined as a signal quality that is acceptable for normal operation.
The M mark is intended to be synonymous with the U mark. The T mark is
intended to be synonymous with the UT mark. The M and T marks are
recommended by the Alliance for Telecommunications Industries Solutions
(ATIS). The U and UT marks are referenced in Section 20.19 of the FCC Rules.
The HAC rating and measurement procedure are described in the American
National Standards Institute (ANSI) C63.19 standard.